The new generation 3D video adopts multi-view video plus depth as the main format. To improve the coding performance and quality of synthesized views

several new techniques

including depth modeling mode

segment-wise DC coding

and skip intra mode

are introduced into the current 3D-HEVC test model for depth intra coding. However

these tools dramatically increase computational complexity

which obstructs the practical applications for the 3D video. Thus

in this study

a fast depth intra coding algorithm is proposed to alleviate the burden of the encoder. Considering that 3D-HEVC reuses the well-known hierarchical coding structure

the mode information of the parent coding units (CU) can be reused to predict the most probable modes for the current CU. Consequently

only a subset of the intra mode candidates is employed to calculate the rough rate-distortion cost. According to rough modes and their rough costs by rough mode decision

the current CU will be classified into three categories

namely

smooth

directional

and edge. For each class

a different set of rough mode candidates will be selected. Simulation results show that the proposed algorithm achieves a reduction of 44% encoding time for depth intra coding while maintaining the quality of synthesized views

compared with the original test model HTM-13.0. Based on the mode information of parent CU and rough mode decision

the proposed method can significantly reduce the number of intra mode candidates. Consequently

the proposed method can provide a remarkable time reduction of depth intra coding with a negligible BD rate increase.